The purpose of this research is to study side effects and safety of a new H5N1 flu (bird flu) vaccine and to look at how well people's immune systems make antibodies to fight infection after they get the vaccine. Up to 300 healthy people who are working at Aventis Pasteur H5N1 virus vaccine production facility in Swiftwater, PA, during the flu season are being asked to participate. It is important for vaccine production workers to receive the vaccine in order to minimize the risk of this bird flu virus combining with the regular flu virus. Volunteers in this study will have a medical screening, 2 vaccinations a month apart, 2 blood sample collections (1 before and 1 after the vaccinations to compare), 5 clinic visits, and follow-up over 6 months. They will also complete a diary card and to write down their temperature once a day and any symptoms they have every day during the week after they get their second shot. They will also be asked to write down any drugs or medicines they take.